1. Field of the Invention
The present invention relates to a motor controller having an abnormality detection function of a power transmission unit between a motor and a main shaft.
2. Description of Related Art
For a machine tool, detection of an abnormality such as a slip which occurs at a power transmission unit such as a belt which transmits a rotational power of a motor to a main shaft has conventionally been performed.
For example, Japanese Unexamined Patent Publication No. 2010-137310 describes a device for detecting abnormality of a belt by using a sensor detecting load information of a motor and a state of a driving belt.
For example, Japanese Unexamined Patent Publication No. S61-103750 describes an abnormality detecting method in which the rotation speed of a main shaft and the rotation speed of a motor are compared, and when the difference between the rotation speed of a main shaft and the rotation speed of a motor deviates from a speed difference for which a speed reduction ratio prescribed between the motor and the main shaft is taken into consideration, it is determined that an abnormality has occurred in a power transmission unit between the main shaft and the motor.
For example, Japanese Unexamined Patent Publication No. 2003-94289 describes an abnormality detecting method in which a slip ratio is calculated by monitoring the rotation speed of a main shaft and the rotation speed of a motor to detect a slip which deviates from predetermined conditions.
For example, Japanese Unexamined Patent Publication No. 2005-246534 describes a method in which an instructed number of revolutions of a controller and an actual number of revolutions of a main shaft are compared, and when a state in which the ratio exceeds an allowable value continues for an allowable time, the state is judged to be abnormal to stop a main shaft motor.
For example, there is an abnormality detecting method comprising a means for detecting a one-rotation signal which outputs a signal every time a main shaft rotates once, in which the change amount of the rotation angle of a motor between the time when the one-rotation signal is detected and the time when the next one-rotation signal is detected is calculated, and when the change amount of the motor rotation angle between every one-rotation signals deviates from predetermined conditions, it is determined that an abnormality has occurred in a power transmission unit between the main shaft and the motor.
In the method in which an abnormality of a power transmission unit such as a belt or a gear between a main shaft and a motor is detected by using a comparative result between the rotation speed of the main shaft and the rotation speed of the motor, for eliminating an influence of a momentary slip in the power transmission unit, it is needed to apply a filter to the speed difference between the rotation speed of the main shaft and the rotation speed of the motor and to perform an abnormality detection process by using data after applying the filter. However, there is a problem that a detection delay due to the time constant of the filter occurs and it takes time to detect an abnormality particularly when the motor and main shaft rotate at a high speed.
On the other hand, in a method in which an abnormality of a power transmission unit between a main shaft and a motor is detected by using a change amount of the motor rotation angle between every one-rotation signals of the main shaft, a delay in detecting an abnormality when the motor and main shaft rotate at a high speed is small since the above-mentioned filter is not needed to be applied. However, there is a problem that a delay in detecting an abnormality may occur when the motor and main shaft rotate at a low speed since an abnormality detection process is performed only when a one-rotation signal is detected.